An international review of the NPF tiger prawn assessment agreed with the conclusions of the 2001 assessment that tiger prawn stock levels were critically low, especially for brown tiger prawns. The 2002 assessment further concluded that brown tiger prawn levels were too low and also emphasized the critical need for an independent monitoring program given the confounding and complexities of the catch rate data used as the sole index of abundance in the NPF assessments. The 2003 assessment suggests that brown tiger prawn stocks are recovering but, given the high level of uncertainty in the assessment, this recovery needs to be independently tested.

The survey data used to determine the initial design for this project (see Background) was more than a decade old and did not cover the full study area. Since the first survey, changes have been made to the survey design to improve the accuracy of the abundance estimates obtained from the surveys. This design needs to be further developed and tested. Work has also begun on developing methods for incorporating the results of the surveys into stock assessments, but more research is required to overcome several technical difficulties encountered.

In this proposal, the CSIRO salaries associated with testing the survey design and with developing new methods of incorporating the results into stock assessments are seen as research. We are therefore requesting about $47,000 from FRDC’s MOU funds. For this reason, CSIRO is also supporting the project to the scale of about $86,000. The remainder of the project, some $520,000, will be underwritten by the industry as agreed in NORMAC, June 2003. The industry and NORMAC have also re-affirmed the long-term need for regular industry-funded monitoring surveys based on the output of this project.

There is a need to provide an updated design for the NPF that would work in the long-term to provide indices of abundance for key species and enhance a difficult-to-use commercial catch rate series. Furthermore, this design needs to address target, byproduct and possibly some effects-of-trawling issues to make the best use of the surveys.

Management arrangements for the NPF tiger prawn fishery are currently chosen so that the spawning stock biomass should recover to the level at which Maximum Sustainable Yield, MSY, is achieved with more than 70% certainty by 2006. MSY is a management reference point that is based solely on biological considerations. From an economic point of view (one that seeks to maximize economic efficiency and fishery returns) this target is inappropriate. The current rebuilding strategy implies that the NORMAC may, over time, be able to reassess the present harsh management measures instituted in the NORMAC agreed effort reduction program in 2001. However, in recent years it has become clear that the fishery is unable to wait for prawn recovery without addressing economic efficiency. NORMAC has identified an urgent need for a further fishery restructure (without compromising biological recovery) so as to maintain economic sustainability and profitability.

An immediate need is for this project to quantify the size of the fleet and length of the season given the biology of ALL the prawn resources. At present it is only broadly possible to answer this question if prawns other than tiger prawns and within year dynamics are ignored (which is unacceptable).

Additionally, this prawn fishery still needs to keep track of its fishing impacts. The main method in the past, with much success, has been through bycatch reduction by TEDs and BRDs. It is now possible, also to include fishing impacts in the modelling mechanisms to allow broader and better informed decision making.

Management advice provided by the NPF Assessment Group needs to take account of the impacts on the stock, economic efficiency and the ecosystem. Input controls are such that several different combinations of fleet size, gear size and season length can produce the same biological outcome but these options would not be equally economically efficient. It is not only overall effort levels that matter for economic efficiency but the manner in which vessels combine inputs in harvest that matters for economic efficiency. This decision over input combinations is sensitive to management decisions and as yet there is no clear economic evaluation of the fishery efficiency under current management practices in a combined biological and economic study.

Limit and target reference points, such as the MSY, in this fishery have only been investigated from the point of view of tiger prawn sustainability. It has been shown in other parts of the world that choosing management arrangements so that fishing effort corresponds to MSY does not necessarily lead to the highest profits and, in fact, lower effort levels generally lead to larger profits and more efficient outcomes. Furthermore, fishing below MSY may also benefit bycatch and byproduct species.

There is therefore a need that future stock assessment undertakes a holistic management view of this prawn fishery. Reference points and management advice should be aimed towards maximising economic return, while ensuring long term target species sustainability and minimising the impact of this fishery on other species wherever possible.

This can only be achieved by:
a) joining the databases held separately by AFMA, CSIRO and ABARE/ANU, and
b) combining the Management Strategy Evaluation frameworks produced by CSIRO on tiger prawns (FRDC 2001/002), ANU/ABARE on economic efficiency (FRRF) and CSIRO investigating effects of trawling on the seabed (FRDC 2002/102).

Need for trawl mapping
Information on where trawling does and does not occur is needed by fishery managers, industry, GBRMPA and others to inform debate and decision making for the trawl fishery. By June 2002, VMS will have recorded all Queensland trawl effort (except the Moreton Bay fishery) every hour for 18 months. These data can be used to map the distribution and intensity of trawling better than ever before. These maps are required by July 2003 for implementation of the Queensland Trawl Plan. Such maps are also needed to model the ecological effects of trawling, since untrawled areas may provide refuge for some vulnerable bycatch species. Such maps will also help assess the required 40% reduction in bycatch.

Need to develop stock assessment and management for ESD
The Trawl MAC have named stock assessment and Review Events as their top research priorities, and VMS research as a high priority. There is a need to improve abundance indices, currently based on CPUE from trawl shots defined as square CFISH grids (6’ by 6’ or 30’ by 30’). This is unrealistic and can lead to significant errors in stock assessment. There is also a need to investigate the way targeting and depletion of aggregations interact with economic factors to affect CPUE.

We can meet these needs using effort and density indices at fine spatial and temporal scales, by using the functionality of newly developed commercial software to develop our modelling systems. Matrices of stock abundance in space and time can be mapped (see attached map) or used in stock assessment models. A major area of research need with the OceanFARM software is user definition of trawl signature and catch distribution functions, which differ between sectors of the trawl fishery.

The functionality must be integrated into the overall management and assessment strategy for each fishing sector. There is potential to substantially improve the reliability of stock assessments.

The Queensland East Coast Trawl Fishery Management Plan, was completed and introduced on 21st December, 2000, with the Management Plan’s Regulatory Impact Statement released October 2000. The plan sets performance criteria for a 40% reduction in bycatch and a 25% reduction in damage to benthos. Environment Australia also sets criteria on the sustainability of (1) target species, (2) retained bycatch (by-product), and (3) discarded bycatch species from trawl fisheries; a key factor of which is the total mortality on these species caused by the fishing operation. FRDC are currently funding QDPI research (FRDC#2000/170) to describe and quantify trawl bycatch in Queensland and the preliminary effects of bycatch reduction devices (BRDs) on the bycatch.

“Hoppers” are product-quality and cost-efficiency enhancement devices that are being progressively introduced into the South Australian, Western Australian, and Northern Prawn Fishery, and have been fitted by a small number of trawlers on the Queensland East Coast. These devices are recommended in the 1997 QCFO (QSIA) sponsored ISO Best Practice manual for onboard handling of prawn catch. Anecdotal reports suggest that these devices not only enhance product quality but significantly increase the survival of bycatch species that are caught by the trawl net (despite BRD’s), because the catch is dropped into a tank of fresh sea-water rather than onto a dry sorting-tray.

Therefore there is a need to pro-actively evaluate and document the effect of Hoppers on survival of discarded bycatch to ensure that the Queensland Prawn Trawl fleet gains maximum recognition for the “environmental credits” accrued as Hoppers are progressively introduced. This would provide an added bonus to a process already underway as a commercial evolution in trawl fisheries around Australia. Such information could also act as an environmental incentive, apart from the product quality and cost consideration, for trawler operators to fit Hoppers.

There is a particular need in the case of the smaller inshore boats involved in the Queensland East Coast banana fishery. Here there is considerable community pressure for inshore closures to cover local and tourist destination beaches, in response to discarded bycatch washing up after trawling operations. Appropriately sized non-mechanised Hoppers are currently under development but these will need to be independently evaluated to ensure that the community is satisfied that they will reduce bycatch mortality, ie no dead fish on politically sensitive beaches.

It is unknown whether the current apparent failure of the stocks to recover in the NP Tiger fishery is related to limited management options, serial depletion of stocks or to the use of the now somewhat discredited MSY and EMSY management targets (see, for example, Larkin, 1977 and summaries in Pitcher & Hart, 1982).

In two recently completed FRDC projects (FRDC 95/014 and 98/109), a preliminary attempt at stock-based assessments was undertaken. These show that some stocks are much more depleted than the single-stock model would suggest. There is a need to clarify which areas are most affected and why these are performing so poorly. There is also a need to develop a multi-stock operating model to open a new direction for modelling in the NPF. This technically complex model would have the potential to benefit the management of benthic crustacean species worldwide. (It should be noted that no operating model, particularly not a spatially explicit one, has been developed for any prawn fisheries in Australia.)

In species, such as prawns, whose dynamics are dominated by yearly recruitment variation, the MSY may well give a false expectation of stability. Management targets that relate to present conditions rather than to equilibrium conditions (e.g. a target fishing mortality rate) may better serve intrinsically variable fisheries, such as prawns. However, reference points developed worldwide have concentrated on output controlled management systems. Given AFMA’s requirement to satisfy its ESD objective, there is therefore a need to consider uncertainty explicitly and to identify performance indicators and harvest strategies that are as robust as possible to incorrect assumptions and estimation errors deriving from limited data. Most importantly, these should be developed in the context of spatially explicit stock assessment models and an input controlled management system.